.\" Copyright 2020, Mike Christie <mchristi@redhat.com>
.\" Copyright 2020, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright 2024, Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH PR_SET_IO_FLUSHER 2const 2024-06-01 "Linux man-pages 6.9.1"
.SH NAME
PR_SET_IO_FLUSHER
\-
change the IO_FLUSHER state
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/prctl.h>" "  /* Definition of " PR_* " constants */"
.B #include <sys/prctl.h>
.P
.BI "int prctl(PR_SET_IO_FLUSHER, long " state ", 0L, 0L, 0L);"
.fi
.SH DESCRIPTION
If a user process is involved in the block layer or filesystem I/O path,
and can allocate memory while processing I/O requests it must set
.I state
to 1.
This will put the process in the IO_FLUSHER state,
which allows it special treatment to make progress when allocating memory.
If
.I state
is 0,
the process will clear the IO_FLUSHER state,
and the default behavior will be used.
.P
The calling process must have the
.B CAP_SYS_RESOURCE
capability.
.P
The IO_FLUSHER state is inherited by a child process created via
.BR fork (2)
and is preserved across
.BR execve (2).
.P
Examples of IO_FLUSHER applications are
FUSE daemons,
SCSI device emulation daemons,
and daemons that perform error handling
like multipath path recovery applications.
.SH RETURN VALUE
On success,
0 is returned.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
.I state
is not a valid value.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 5.6.
.SH SEE ALSO
.BR prctl (2),
.BR PR_GET_IO_FLUSHER (2const)
